A coded (double-blind) study of platelet transfusions or platelet-free plasma transfusion allocated at random continues with thrombocytopenic patients with acute leukemia. Emphasis at present is on the therapeutic arm of the study, by double-blind techniques, as well. However, the degrees of histocompatibility of donor-recipient are being evaluated to assess the role of tissue typing in platelet and adjunct leukocyte (granulocyte) transfusion effectiveness in acute leukemia. BIBLIOGRAPHIC REFERENCES: Higby, D.J., and Henderson, E.: Granulocyte transfusions for infection during neutropenia: A Review. Seminars in Oncology 2: No. 4, 361-368, 1975. Higby, D.J., Freeman, A., Henderson, E.S., Sinks, L. and Cohen, E.: Granulocyte transfusions in children using filter-collected cells. Cancer (in press) 1976.